7 research outputs found
Terahertz investigations on photoisomerisable compounds
<p>We performed computational terahertz studies on organometallic photoisomerisable compounds, employing both gas phase and solid phase calculations. The calculations demonstrate the potential of employing terahertz techniques on photoisomerisable compounds. In particular, the <i>trans</i>-ligand, counterion and crystal effects are evaluated via the density functional theory calculations. In order to fully understand the terahertz responses of the photoisomerisable compounds, their experimental terahertz spectra were obtained and compared to the calculations. The calculated spectra generally predict the experimentally observed absorption peaks, while combined gas phase and solid phase calculations offer better agreement with the experiments. The first principles calculations also reveal the sensitivity of terahertz signal on the photoisomerisation processes, suggesting a photo-terahertz set-up that could be built in the future to fast screen and fully understand the photoisomerisable compounds, for related applications such as photo-transducer and photo-switch that require photoinduced geometrical changes.</p
First-Principles Study of Molecular Adsorption on Lead Iodide Perovskite Surface: A Case Study of Halogen Bond Passivation for Solar Cell Application
Organic
molecules have recently been used to modify the surface/interface
structures of lead halide perovskite solar cells to enhance device
performance. Yet, the detailed interfacial structures and adsorption
mechanism of the molecular modified perovskite surface remain elusive.
This study presents a nanoscopic structural view on how organic molecules
interact with the perovskite surface. We focus on the halogen bond
passivated lead iodide perovskite surface, based on first-principles
calculations. Our calculations show that organic molecules can interact
with the perovskite surface via halogen bonds, which modifies the
interfacial structures of the perovskite surface. We also constructed
a detailed potential energy surface of the perovskite surface by moving
the adsorbed molecule along different axes of the unit cell in order
to comprehensively understand perovskite surface structures. This
study demonstrates the effectiveness of modifying the perovskite surface
structure via a molecular adsorption approach, and anticipates that
the properties of perovskite materials can be further improved by
a molecular engineering method
N–Co–O Triply Doped Highly Crystalline Porous Carbon: An Acid-Proof Nonprecious Metal Oxygen Evolution Catalyst
In comparison with nonaqueous Li–air
batteries, aqueous Li–air batteries are kinetically more facile
and there is more variety of non-noble metal catalysts available for
oxygen electrocatalysis, especially in alkaline solution. The alkaline
battery environment is however vulnerable to electrolyte carbonation
by atmospheric CO<sub>2</sub> resulting in capacity loss over time.
The acid aqueous solution is immune to carbonation but is limited
by the lack of effective non-noble metal catalysts for the oxygen
evolution reaction (OER). This is contrary to the oxygen reduction
reaction (ORR) in acid solution where a few good candidates exist.
We report here the development of a N–Co–O triply doped
carbon catalyst with substantial OER activity in acid solution by
the thermal codecomposition of polyaniline, cobalt salt and cyanamide
in nitrogen. Cyanamide and the type of cobalt precursor salt were
found to determine the structure, crystallinity, surface area, extent
of Co doping and consequently the OER activity of the final carbon
catalyst in acid solution. We have also put forward some hypotheses
about the active sites that may be useful for guiding further work
High Electrochemical Performance of Monodisperse NiCo<sub>2</sub>O<sub>4</sub> Mesoporous Microspheres as an Anode Material for Li-Ion Batteries
Binary metal oxides have been regarded as ideal and potential
anode materials, which can ameliorate and offset the electrochemical
performance of the single metal oxides, such as reversible capacity,
structural stability and electronic conductivity. In this work, monodisperse
NiCo<sub>2</sub>O<sub>4</sub> mesoporous microspheres are fabricated
by a facile solvothermal method followed by pyrolysis of the Ni<sub>0.33</sub>Co<sub>0.67</sub>CO<sub>3</sub> precursor. The Brunauer–Emmett–Teller
(BET) surface area of NiCo<sub>2</sub>O<sub>4</sub> mesoporous microspheres
is determined to be about 40.58 m<sup>2</sup> g<sup>–1</sup> with dominant pore diameter of 14.5 nm and narrow size distribution
of 10–20 nm. Our as-prepared NiCo<sub>2</sub>O<sub>4</sub> products
were evaluated as the anode material for the lithium-ion-battery (LIB)
application. It is demonstrated that the special structural features
of the NiCo<sub>2</sub>O<sub>4</sub> microspheres including uniformity
of the surface texture, the integrity and porosity exert significant
effect on the electrochemical performances. The discharge capacity
of NiCo<sub>2</sub>O<sub>4</sub> microspheres could reach 1198 mA
h g<sup>–1</sup> after 30 discharge–charge cycles at
a current density of 200 mA g<sup>–1</sup>. More importantly,
when the current density increased to 800 mA·g<sup>–1</sup>, it can render reversible capacity of 705 mA h g<sup>–1</sup> even after 500 cycles, indicating its potential applications for
next-generation high power lithium ion batteries (LIBs). The superior
battery performance is mainly attributed to the unique micro/nanostructure
composed of interconnected NiCo<sub>2</sub>O<sub>4</sub> nanocrystals,
which provides good electrolyte diffusion and large electrode–electrolyte
contact area, and meanwhile reduces volume change during charge/discharge
process. The strategy is simple but very effective, and because of
its versatility, it could be extended to other high-capacity metal
oxide anode materials for LIBs
Molecular Engineering of the Lead Iodide Perovskite Surface: Case Study on Molecules with Pyridyl Groups
We computationally
investigate the molecular engineering approach
of the lead iodide perovskite surface employing a pyridyl anchor-based
molecular adsorbate as an example. The molecular adsorption approach
on lead halide perovskite surfaces has been employed for passivation
purposes in perovskite solar cells and was demonstrated to successfully
enhance the solar cell performance in previous experimental studies.
It is an open question whether the structures and properties of the
lead halide perovskite can be further modified via the molecular engineering
approach, and this study serves to probe the molecular engineering
approach in the lead halide perovskite surface. First-principles calculations
are employed to determine the nanoscopic structure of the lead halide
perovskite surface with pyridyl anchor-based molecular adsorbates
and prove that the pyridyl anchor-based molecule resides stably on
the perovskite surface and modifies the perovskite surface structure.
In addition, the calculations demonstrate that the electronic and
optical properties of the lead halide perovskites can be controlled
by the molecular engineering method. Noteworthily, we find that the
molecular engineering approach is effective to modify the optical
properties of the lead halide perovskite layer investigated in this
study. Such molecular engineering approach on the perovskite surface
could be potentially applicable to further enhance the performance
of perovskite solar cells and perovskite-based optoelectronic devices
Hollow MnCo<sub>2</sub>O<sub>4</sub> Submicrospheres with Multilevel Interiors: From Mesoporous Spheres to Yolk-in-Double-Shell Structures
We present a general strategy to
synthesize uniform MnCo<sub>2</sub>O<sub>4</sub> submicrospheres with
various hollow structures. By using MnCo-glycolate submicrospheres
as the precursor with proper manipulation of ramping rates during
the heating process, we have fabricated hollow MnCo<sub>2</sub>O<sub>4</sub> submicrospheres with multilevel interiors, including mesoporous
spheres, hollow spheres, yolk–shell spheres, shell-in-shell
spheres, and yolk-in-double-shell spheres. Interestingly, when tested
as anode materials in lithium ion batteries, the MnCo<sub>2</sub>O<sub>4</sub> submicrospheres with a yolk–shell structure showed
the best performance among these multilevel interior structures because
these structures can not only supply a high contact area but also
maintain a stable structure
Photoassisted High-Performance Lithium Anode Enabled by Oriented Crystal Planes
Lithium (Li) metal anodes are candidates for the next-generation
high-performance lithium-ion batteries (LIBs). However, uncontrolable
Li dendrite growth leads to safety issues and a low Coulombic efficiency
(CE), which hinders the commercialization of Li metal batteries. Stable
Li anodes based on the tailored plane deposition and photoassisted
synergistic current collectors are currently the subject of research;
however, there are few related studies. To suppress the growth of
Li dendrites and achieve dense Li deposition, we design a low-cost
customized-facet/photoassisted synergistic dendrite-free anode. The
tailored (002) plane endows it with a nanorod array/microsphere composite
structure and exhibits a strong affinity for Li, which effectively
reduces the Li+ nucleation overpotential and promotes uniform
Li deposition. Notably, during the photoassisted Li deposition/stripping
process, due to electron–hole separation, a weakly charged
layer is formed on the (002) surface and local charge carrier changes
are induced, reducing the overpotential by 8.3 mV, enhancing the reaction
kinetics, and resulting in a high CE of ∼99.3% for the 300th
cycle at 2 mA cm–2. This work is of great significance
for the field of next-generation photoassisted Li metal anodes